Radio transmitting and receiving system



June 25, 1946. F. M. DAvls RADIO TRASMITTING AND RCEIVING SYSTEM Filed Feb. 28, 1944 2 Sheets-Sheet 1 June 25, 1946.

F. M. DAvls 2,402,606

RADIO TRANSMITTING AND RECEIVING' SYSTEM Filed Feb. 28, 1944 2 Sheets-Sheet 2 f ,lzvwzn Ffa/1% j vac):

Patented June 25, 1946 `ARADIO TRANSMITTING AND RECEIVING SYSTEM Frank M. Davis, Cedar Rapds,=Iowa, assignor to Collins Radio Company, a corporation of Iowa Application February 28, 1944, Serial No. 524,205

(Cl. Z50-13) 7 Claims.

This invention relates to a radio transmitting and receiving system, and-more particularly to a system ensuring transmission and reception on the same frequency.

One feature ofthisuinvention isthat itprovides :an `improved radio ktransmitting and receiving system anotherifeaturetof this invention is thata single tuning `means Yeffectscoordinated selection of a desired selected frequency in both thetransmittingtandreceiving iportions of the system;` stillianotherfeatureof this invention is .thattransmissionl and reception take place on the'same frequencyvdespite anyvariation of oscillator frequency from vits calibrated frequencies; yet another feature of this invention is that the system is readily tunable to` any desired frequencyin any of apluralityof frequency ranges; and a further feature of 4this invention is that an intermediate :frequency amplifier tunable over onlyta single band-is adaptedto be operative for `reception in any of the frequency.l ranges. 'Other features and advantages of this invention will be apparent from the following specification and the drawings, in which:

`Figure 1 is alblock diagram of a system/embodying my invention; and *Figurer 2, comprising the'portions 2a andb, vis=a circuitdiagramk of an operable embodiment l:of i a transmitting and receivingsystem `corresponding'to the diagram of 'Figure l. 4

'Iwo-wayradio communication isfbecoming of increasing importance,and under manycircumstances it is desirable to have the transmitting and receiving equipment tunable overa desired frequency range, 'ora plurality of frequency ranges. Under such conditions the transmitted frequency cannotl be crystal controlled,' but 'must haveja frequency'controlled-bya tunable oscillator tank circuit. Despitev the `greatest care in kdesign and construction, anoscillator'tankv circuit undergoes frequency 4changes as the result of its-exposure to variations in temperature, humidity.-r etc.,and 4this* makes it' difficult to determine -faccuratelyby'anyfsystemcf dial calibration, the

frequency being `transmitted 'or received, Vparticularly in' the higher frequency bands,A as those "used inV aircraft Work.

frequency'areenSured. "This enables `an operator to tune in on another station which is transmitting; and then togoo'n thelair himself asfsoon -v as the other's'tation ceases transmission withi full assurance that hissign'al fison' thesamefrequency as that on which the other station was transmitting, regardless of the setting of his tuning `dial or the accuracy of its calibration. The system which I am here disclosing and claiming is a variation of and an improvement on-a system for achieving the desired result by displacement of the oscillator frequency a given percentage, the broader idea being the subject matter of a copending application of Arthur A. Collins, Serial No. 524,204, filed Feb. 28, 1944. The desired result of transmitting and receiving on the same frequency by a single-control arrangement may also be secured by other systems which are the subject matter of other copending applications of myself and of Melvin L. Doelz, Serial No. 548,978, filed August 11, 1944, and Serial No. 524,206, filed February 23, 1944, respectively, my other said application containing broad claims generic to the systems shown in this and all of the other above-mentioned applications.

My system comprises, as its principal elements, wave generating means variable over a plurality of `predetermined frequency ranges, as atunable oscillator with associated frequency multiplying means; means for amplifying and transmitting Waves of a selected frequency in any of said ranges; means for displacing the frequency of the waves by predetermined given percentages (rather than by a given frequency), these percentages having a certain ratio to the multiplication factor thereafter used; and a super-heterodyne receiving system having an intermediate frequency amplifier tunable over a certain band, tuning of the oscillator and the intermediate fref quency amplifier being ganged or coordinated' by operation of a single tuning control, and the displaced Waves serving as the local heterodyning Waves. for the receiving system. When one has ceased transmitting, rendering the displacing means and system operative Without touching the tuning control ensures reception on the exact frequency being previously transmitted; and conversely, when one has finished receiving another signal, switching to transmission ensures sending on the exact frequency of the signal previously heard, regardless of any differences between actual oscillator frequency and dial setting.

While I am terming the system disclosed here a single-control system it will be understood it is :meant that there would be only a single tuning control for both the transmitting and receiving portions of the system, which would normally be housed in a single cabinet. In addition; of course, there would be a band switch, antenna rcouplingand loading controls, an on-off switch or erated by the closing of a single contact.

y several of such switches, and generally a` manual volume control for the receiving portion of the system. rihe switch-over from transmission to reception would normally be effected by a keying relay, or by a push-button-operated relay associated with the microphone of the transmitter. With a system of this kind, no matter how inexperienced the operator may be, once he finds and hears a given station (whether it be another airplane, a ground station, or the like) he is sure to be able to talk to it, sure to be on the frequency to which the receiver of that other station is tuned. Another advantage, claimed in one of the other co-pending applications (my application Serial No. 548,978, led August l1, 1944), is that the same antenna tuning and loading circuit may be used for coupling both. the transmitter and receiver to the antenna, so that the antenna can be tuned during reception, without breaking radio silence, with assurance that transmission will be at or very near maximum possible power without loss of time for adjustment of the antenna tuning and loading controls after transmission has been started.

In the particular embodiment of my system illustrated here, and referring first more particularly to the block diagram, Figure l, a tunable oscillator A delivers its output to a rst multiplier B, this output being delivered in turn to a second multiplier C, these comprising means for generating Waves of any desired frequency in any of a plurality of bands, the multipliers being adapted to provide an output which bears a relation to the oscillator output resulting from multiplication by a factor of anything from unity up to about 20. The output of the multiplier C is connected to the movable element of a. two-position switch C (show-n in the transmitting position in dotted lines and in the receiving position in solid lines), being delivered to the power amplier D during transmission. The amplified carrier wave is modulated in conventional manner bya lmodulator here identified as E. The modulated output of the power amplifier is connected through another switch D (in its transmitting position) to the tunable antenna tank and loading network F, this being in turn connected to the antenna and to ground. This arrangement `comprises a conventional tunable transmitting system.

The oscillator has associated with it another transmission-reception switch A' adapted to connect another Xed reactance element into the tank circuit of the oscillator and to disconnect it therefrom, to displace the frequency of the oscillator afdesired percentage. In this particular system, illustrated as designed for use on four bands, any of four fixed condensers (determined by the band switch A") is thrown into or out of circuit, as desired, by the switch A. The transmission-reception switches throughout the system, as the switches A', B and C', are ganged so that they operate in synchronism, generally by a relay op- The movable elements of these three switches stand in the position shown in solid lines for reception,

. and moveto the position shown in dotted lines for transmission.

Wlhen the system is switched from transmission to reception, without touching the tuning control,

operative. For example, the displacement condenser'used on the first band might have such a 4 relation to the fixed condenser in the oscillator tank circuit as to result in a frequency displacement of 10%; that used in the second band might provide a displacement of 5%; that in the third band, a displacement of 31/3%; and that in the fourth band, a displacement of 2%. With the transmission-reception switches set for reception, thel output of the multiplier C is delivered to the tunable filter G, which is tuned to and designed to pass only the displaced frequency; the antenna and its associated network are connected through the switch D to the input of the radio frequency amplifier I-I; and the output of this amplifier H is delivered to the mixer or first detector stage J where the displaced wave from the wave generating means, delivered through the tunable filter G, serves as the local heterodyning wave to beat the incoming signal down to an intermediate frequency. The reduced frequency signal is delivered to the tunable intermediate frequency amplifier K and then passes through a second detector L and an audio amplifier M, where it is delivered to some translating means, as earphones, not shown. l

In any particular band or frequency range, the difference between the desired incoming signal and the displaced frequency wave delivered to the mixer J varies (in the sense of absolute frequency) as a result of variations in the frequency of the wave generating means, That is, the same percentage displacement results in a greater frequency difference at the upper end of the oscillator tuning range than at the lower end, which in turn results in the frequency of the beat f note; and to take care of this intermediate frequency variation, the intermediate frequency amplier is made tunable. As illustrated'in the block diagram, the tuning controls of all of the tunable portions of the system are ganged. The gauging and tracking of the intermediate frequency` amplifier tuned circuit with the oscillator tuned circuit may be` done accurately, the circuits .being of the same type, and there not being the problems present in accurate tracking of xed frequency displacement arrangements, where tracking is Yusually accurate at only two or three points. The various tuned circuits are provided with different xedreactance elements adapted to be switched in when different bands are to be covered, of course, the coordination being effected by tracking of the variable reactance elements,

and not being lost or disturbed by the addition and subtraction of fixed reactances of the opposite character.

For the purposes of this description it will be assumed that the oscillator A is so designed as to be variable over a range of 1,000 to 1,500 kc. during transmission; and that operation of the frequency displacing switch A results in the oscillator tuning'through a different band during reception, a band displaced by a percentage determined by the particular frequency range or band on which the set is operating at that time. In this regard, it will be understood that the word displacement is intended broadly to cover either anincrease or a decrease of frequency throughout the range, and that it can be accomplished by removal or addition of iixedreactance to the tank circuit. For convenience of description, the frequency used for transmission is being termed the initial or desired frequency, and the different frequency used for local heterodyning purposes is being termed the displaced frequency.

.anca-coc cationv factor, transmissionfmay be onany: selected frequency in'ff-t-he range of" 2,000Mtoy 3;'000kc., determined by thefsetting` of vthe tuning control;

.1and=`for pur-posesofillustration'` itmay be asf sumedthatfa signal is being transmitted ori 2,000 kc. On this rstband the additional condenser "used in conjunction -withf thev larger: fixed condenser in the-tank circuit of the oscillatorirmay chave-aly valuel such that operation of the displac- Ifingfswit'ch A* `causes the oscillator frequency to'fbe I displaced Y 10% ,'so thatf at the lower Aend of-the --bandpwhere the tuning control is set, 'the oscil- 'lator frequency is displaced from-1,000 kc. to 1,100J'kc. "In the f particular system vhere being f disclosed, I use ahwavewhich isha differentfmul- 1tiple-for reception than forr transmission, preferab'ly one multi-pleA different. In the caseof `the -first band vor. frequency range of the-system `being described, the multiplication' factor vused for rtransmissionwould be2,A while that used for revception would be 1, the displaced oscillator frefiquencybeing used directly as-theV local heterodyning wave.

`It `will be recalled that transmission vwas yat .a

...frequency of 2,000 kc. `Without vdisturbing-the tuning controls, throwing the set over to receiving #causes displacementfof thel oscillator fre- ,.'quency `to 1,100 kc.; andM-whenv thisvwave is-delivered to themixer of the super-heterodynereceivingv portion yof .the system and 4beat against a 2,000 kc. incomingsignal, theresultant is a- 900 kc; intermediate frequency. rAt the upper end of 4,the range ofthe oscillatorthe transmitted fre- ;quency would-be 3,0001kc.; the` displaced or local heterodyning frequency 1,650 kc., so that the in- .termediate .frequency would be 1,350 kc. v.That is, -.the"intermediate frequency :amplifier of there- '..ceiving'portion of thev system `must bemade tunable overa band from900 to 1,350 kc., in this par- -ticular case.

Othersundesiredrsignals of an initial frequency such that they would beat to-this same .intermediate frequency would `be eliminated -by the tuned` circuits inztheradio'frequency porx tions-of the receiving system, in 1 accordance kwith .general practice, sothat the frequency received wouldbe exactly` the same: as that transmitted. This is merely a'function of the properisetting andtracking ofthe various circuits of the'iset, l something Whichucanv be done' `during manufac- -turinguor in service fand :maintenance depots, 'and the operator .isffalwaysassured that .he is transmitting and receiving on the same frequenvcy,--whether or not temperature or other. variables --cause.that frequency to be di'erentfrom they frequency indicated by his tuning dial.

:Four representative bands of frequency ranges,

rand the oscillator and multiplier output frequencies,V are shown in the following table:

Percent L Interme- Osclllator Multiplier 1, OOO-1, 500 2 000.37 000 tgggg 10 Lfion-1,650 l 900-1350 1 I ,ooo-4,500 1,05c1j575 l! 5 {2,100-3, 15o 900%350 iiggg-ij l 3M @004.350 1, ooo-1,500 HY 000 1,020-L530 2 s100-7,650 90o-1,350

Itiwill be .noted that the ratio of the percentage displacement used in various bands is the recip- Mrocal of .the ratio fof the multiplication factor used for the local heterodyning wave;` and this :Limltiplication:factor is different .from` that used for` transmission,n generallyfonefless. Themultieffected in either case by a small xed reactance kc vcentages `of displacement in the different bands each condenser.

yerating conditions. tank circuits throughout the system arershown `plication factor in the -second band (for the local heterodyne wave) is 2 while thatfor the firstband is 1;-and 5% displacement is used in thef second band as compared with10% in the first band. This results in the same absolute frequency shift or displacementof the waves at any either of these tuned circuits and theyfare easily ganged and tracked. Obviouslma different multiple would not have to be used for the local Y heterodyne waves, but the same .multiple could be used and the percentage ratio so chosen that the intermediate frequency :bands still 'need only `be tunable over a single range. f displacement and doublingwere used for the local For example, if 10% heterodyne waves in the rst band, thiswould Yprovidea multiplier output ofx2,f2003,300 kc., v.which would lrequire an intermediate frequency amplifier tunablel from 20G-300 kc. Itvwould f then be necesasry to use a fig/3% displacement in the secondv bandwhich, with tripling,rwould= give a local heterodyning frequency of. 3,200-4g800-kc.,

or again an intermediate frequency of.l200-.300

In any event, the ratio of the various pershould be the reciprocal of the ratios of the mull tiplication factors used for the local heterodyning waves in order to vuse a single intermediate frequency amplifier tuning band.

Referring. now kmore particularly to the circuit diagram of Figure 2 (comprising portions. 2a and l2b), .the portions corresponding to the'various rectangles of the block diagram of Figure lv are similarly lettered. The oscillator A isv shown as comprising a tube Iii, which. may be tube type' No.

.12SJ7, having. a tank circuit comprising a permeability tuned variable inductance I I, a fixed con- ,denser I2 permanently incircuit, and additional xed condensers ISa-d adapted to be connected to or disconnected from the tank circuit in' accordance `with the position of the :displacing switch A and the band switches .associatedv with Merely for trimming purposes, another fixed condenser I3e of small capacity is in shunt with the main condenser I2 when the switch A is in its upper or transmittingposition.

It will be understood that the condensers I3a-.d

are so proportioned that, in combination"'with the condenser I2, theygive the desired displacement (on their respective bands) from the frequency generated by the combination of. thecoil II-and the-condensers I2 and I3e. vSince these fixed condensers may all be of the same'type. and

, general character, temperature or other variables will affect them similarly, and the percentage displacements will always stay the same under op- While vthe various tuned as having fixed condensers (xed except for such slight variations as may be desirable for trimming) and variable inductances, it will `be understood that the principles are equally applicable to circuits where the inductances are fixedy and tuned by variable condensers, displacement being During transmission one of the condensers IGa-d (depending upon the position of the band switch associated with them) is in shunt with the coil I5, while during reception a direct connection (on the first band) or a similar one of the condensers I1 is used to provide (with the same setting of the coil I5) a tank circuit tuned to the displaced frequency. The

, output of the multiplier B is delivered to the multiplier C comprising the tube I8 and another similar arrangement of tuned circuits, band switches, transmission-reception switches, etc. These are here identified as comprising the tunable coil I9 and the cooperating sets of condensers and 2|.

As before a direct connection or an appropriate one of the condensers 20 is associated with the coil I9 during transmission when this second multiplier is operative; and a direct connection or an appropriate one of the condensers 2l is associated with the coil when the displaced waves are being delivered, this latter tuning combination providing the tunable filter for delivering the displaced local heterodyning waves to the mixer. While the band switches and transmission-reception switches are distributed throughout the circuit diagram in such a way that, as is the case with the tuned coils, it would be dicult to show that they are ganged, it would be understood that the band switches and the transmission-reception switches are ganged or coordinated, just as the tuning of the various tunable coils throughout the system.

When transmitting, the output of the multiplier section of the system is delivered to the power amplifier here shown as comprising the tubes 22 and 23, which may be of tube type No. 1625, and which would in commercial practice be preceded by a driver stage and possibly also a pre-amplifier stage, these being omitted here for simplicity. The space current in these tubes would be modulated by Waves derived from the i modulating portion of the system, shown in the upper right-hand half of the sheet identified as Figure 2b. This is here shown as comprising a jack 24 adapted to have a microphone or keying means connecting thereto, this being coupled to a driver tube 25, which may be tube type No. 12A6 tube (and which in practice would generally be preceded by a pre-amplifier tube) in turn transformer coupled to modulator tubes 26 and 21, which may of tube type No. 1625, the output of these modulator tubes affecting both the screen and plate voltages of the power amplifying tubes 22 and r23, through the wires c and d. The wire a carries the positive plate supply voltage for the receiving portion of the system, and the Wire b provides the connection between the multiplier tunable filter circuit output and Vone of' the grids of the mixer tube in the super-heterodyne receiving portion of the system.

The modulated output of the power amplifier is delivered, when the switch D' is in its upper or transmitting position, to the antenna tank circuit comprising the condenser 28 and the variable inductance 29. This is coupled, where it is to be used with a short antenna, to antenna loading y8 meanshere shown as comprising a tapped coil 3U and a variometer 3 I, the terminal 32 being adapted to be connected to the antenna.- f

When the systemis thrown over to receiving, the antenna tank circuit is connected, as shown in the drawings, through the wire f to the signal grid of the radio frequency amplifying tube 33, which maybe tube type No.r 12SK7 tube, plate supply for the super-heterodyne receiving system being then provided by a connection through the plate-supply change-over switchN', ganged with the other transmission-receptionY switches. The input of the radio frequency amplifier is, of course,tuned by the vtank circuit here shown as associated with the antenna. The Voutput is tuned by a tank circuit comprising the variable inductance 34 andthe appropriate one of the condensers in the set 35, according to the lposition of the band switch.'

The voutput of the radio frequency `amplifying arrangement is coupled to one of the grids of the mixer tube36; While' another grid of this tube is supplied with the local heterodyning Vor displaced waves derived from the wave generating means comprising the oscillator and multipliers, these waves being delivered through the-wire b, as previously mentioned. The mixer, in accordance with conventional practice, beats the signal frequency down to intermediate frequency which, in the case of the sets of facts assumed above, is in the band comprising o-1,350 kc.

This intermediate frequency output is delivered to an intermediate frequency amplifier K here shown as comprising the tube 31, which may be tube type No. 12SK7 tube, it beingunderstood that in commercial practice at least two similar stages of such intermediate frequency amplication would be used in cascade, one such stage being omitted from this circuit diagram for sim- .plicity of illustration. In accordance with conventional intermediate frequency amplifier practice both the inputs and outputs of a transformer coupling arrangement are tuned; but, contrary to normal practice, these coupled tuned circuits are i tunable over a band, as the 9001,350 kc. band assumed. The input side of the intermediate frequency coupling arrangement is here shown as comprising the tunable coil 38 and the condensers 39, 40 and 4I, this latter condenser being common with the output tank circuit of the arrangement, comprising the other condensers 42 and 43 and the tunable coil 44,

The output of the tube 31 is Vdelivered through Ya fixedly tuned band pass arrangement, here identified in general as 45, designed to pass a SOO-1,350 kc. band, to a detector, beat-frequency-oscillator tube 46, which may be tube type No. 12SR7. The two anodes are connected together to achieve the desired detection function, while the additional grid and plate elements cooperate with the cathode to provide a beat frequency oscillator when desired, this being turned off by opening the on-oi switch 41 when voice is being received. The audio output of the detector tube 46 is delivered to an audio amplifying tube 48, which may be tube type No. lZSK', the output of this tube being here shown as delivered to a jack 49 which is adapted to be connected to any desired translating device, as earphones. In practice it Will be understood thatV the tube 48 would normally be followed by at least one additional power stage of audio amplification.

An operative circuit of the character described and.for the bands and frequency ranges previ- 91; j ouslyvassumed,imightrha .e the oscillator finductance il I variable',stromy f 11-"25;v microhenries ;V the multiplier; c antenna-tanki circuit; and 'mixer inductan'cesrl; I9, .Maand 34variab'l'e from 6.2--14 microhenries; and thev intermediate frequency primary' and secondary inductances variableV from 1'Z5e400V microhetnries: Under these' circumstances, the oscillator tank circuit principal` condenser I2might have afcapacity of 800 micro-microfarads, andthe condenser |3e (associated with `it duringtransmission only) a capacityof 200 micro-microfarads; while the condensers 13a-dmightfhavewcapacities, for the bands assumed, of 28,: 110; 125" and 160`micromicrofarads. The condensers' I .fia-d in the `inputofthe firstmultipliermight have a capacity ofl 450,t 200, 112 and 50-micro-microfarads'; and thesesame values might be' used for the sets of condensers- 28 and v35; while the condensers b-d would have values corresponding to the powerampliiier, and those associatedwith the e tubes 33 and' ,might be .001 microfarad; While that `coupling the detector tube 4B to the tube 48 might be .1 microfarad, andthat-at the input of the oscillator tube 100 micro-microfarads'.

The bi1-pass condensers in the transmitting and' receiving portions of "the system might all be .002 mirrofaradgexcept the condenser in the filament circuit of the tubel48, and those associated with the filaments of the driver and modulating tubes= 25,-I'26Lanld 21, which would preferably be in the neighborhood of 20 microfarads. The screen grid resistors in the multipliers and power amplifier would generally be 10,000 or 20,000 ohms; the grid leak resistors in the oscillator, multiplier, and audio amplifier tubes about 50,000 ohms; that used with the driver tub'e 2'5 about 1/2 megohm; that used with the tube 33 about 1 megohm; and those associated with the signal grid of the mixer and intermediate amplifier tubes from 100,000 to 500,000 ohms. The screen grid resistors used in the receiving portion of the system would preferably be of a higher value than those used in the transmitting portion, and appropriate to the tubes employed, as for example 100,000 ohms, while the cathode resistors would he from 200 to 500 ohms depending upon the tubes and the desired cathode biasing in each portion of the circuit. The other circuit elements not specifically described would follow conventional practice in connection with the types of tubes named in circuits for the purposes Vshown here.

While I have shown and described certain embodiments of my invention, it is to be understood that it is capable of many modifications. Changes, therefore, in the construction and arrangement may be made without departing from the spirit and scope of the invention as disclosed in the appended claims.

VI claim:

1. Radio apparatus :of the character described, including? wave generating ymeans variable `over each of a plurality of predetermined frequency ranges; means for amplifying and transmitting Waves of any selected frequency in any of said ranges;` means for displacing the frequency of the waves different `given percentagesfof the selected frequency in the different ranges;` anda super-heterodyne receiving systemhaving an intermediate frequency; amplifier tunable Vover ya certain band, a-mixer delivering its output to the intermediate frequency amplifier, means for coordinating the variationI ofthe generating means with the tuning of the intermediate frequency amplifier, and means for connecting said mixer to said generatingmeans,wherebyfthedisi placed waves Vserve'as the4 local heterodyning;`

waves for `said receiving system;

2. Radio apparatus of `the characterdescribed,

including: wavegenerating means variable over` eachA of a-.plurality of predetermined frequency ranges; means for Aamplifying..and transmitting wavesof any selected frequency in anyof said-` ranges; means for displacing the frequency of the waves different given percentages of` the selected frequency in the different ranges; anda super-heterodyne receiving system having an intermediate frequency amplifier-tunableover a certain band, a mixer delivering its output tothe intermediate frequency amplifier, means for coordinating the variation of the generating means with theA tuningof the intermediate frequency amplifier, andrfmeans for-connecting said' mixer to said generating means, whereby .the rdisplaced waves serve as the local heterodyning waves forV said receiving` system,` the displacement percentages being soselected that, in all said ranges, the difference between theselected frequencies `and the f local heterodyning `frequencies vis the same and corresponds` to. theband over which the intermediate frequency amplifier is tunable.

Radio apparatus-of the character described, including: wave generating 'means variable over eachof a plurality of 'predetermined frequency ranges; meansfor amplifying` and transmitting,

waves of any selected frequency in any of said ranges; means for displacing the frequency of the waves different given percentages of the selected frequency in the different ranges; a superheterodyne receiving system having an intermediate frequency amplifier tunable over a certain band, a mixer delivering its output to the intermediate frequency amplifier, and means for coordinating the variation of the generating means with the tuning of the intermediate frequency amplifier; and selectively operable means for connecting the wave generating means tothe amplifying means in one operative position and for actuating the displacing means and connecting the wave generating means to the mixer of the receiving system in another operative position, whereby the displaced waves serve as the local. heterodyning waves for said receiving system.

4. Radio apparatus of the character described, including: an oscillator for generating waves of a variable frequency; means for effecting predetermined different multiplications of the frequency of the Waves generated by the oscillator to provide a plurality of predetermined frequency ranges; means for amplifying and transmitting the waves resulting from a selected one of said multiplications; means for displacing the frequency of the waves different given percentages of the selected frequency in the different ranges; and a super-heterodyne receiving system having an intermediate frequency amplifier tunable over a certain band, a mixer delivering its output to the intermediate frequency amplifier, means for coordinating the variation of the generating means with the tuning of the intermediate frequency amplifier, and means for connecting said mixer to said generating means and selecting a different predetermined multiplication, whereby displaced Waves of a multiplication other than that used in transmitting in each said range serve as the local heterodyning Waves for receiving in the same range.

l 5. Apparatus of the character claimed in claim 4, wherein the percentages of displacement of the selected frequency in the vario-us predetermined frequency ranges have a ratio equal to the reciprocal of the ratio of the multiplication of the displaced Waves in the various ranges, so that, in all said ranges, the dierence between the desired frequencies and the local heterodyning frequencies is the same and corresponds to the band over Which the intermediate frequency amplifier is tunable.

6. Radio apparatus of the character described, including: an oscillator having a frequency controlling tank circuit comprising an inductive element and a capacitive element in parallel, one of said elements being variable and the other fixed; means for effecting predetermined different multiplications of the frequency of the Waves generated by the oscillator to provide a plurality of predetermined frequency ranges; means for displacing the frequency of the waves diiferent given percentages of the selected frequency in the different ranges, this means comprising other reactive elements of the same character as the fixed element and means for connecting them into the tank circuit and disconnecting them therefrom; means for amplifying and transmitting i the Waves resulting from a selected one of said multiplications; a super-heterodyne receivingr system having an intermediate frequency ampli- 1 er tunable over a certain band and a mixer delivering its output to the intermediate frequency amplifier; selectively operable means for effecting a given predetermined multiplication and delivering the output thereof to the amplifying means in one operative position and for effecting a selected percentage displacement of the waves, a diiferent predetermined multiplication thereof, and delivery of them to the receiving system in another operative position, whereby the displaced waves serve as the local heterodyning waves for said receiving system; and a single means for effecting coordinated variation of the variable element in the oscillator tank circuit and tuning the intermediate frequency amplifier.

7. Radio apparatus of the character described, including: an oscillator having a frequency controlling tank circuit comprising an inductive element and a capacitive element in parallel, one of said elements being variable and the other fixed; means for effecting predetermined different multiplications of the frequency of the Waves generated by the oscillator to provide a plurality of predetermined frequency ranges; means for displacing the frequency of the Waves different given percentages of the selected frequency in the different ranges, this means comprising other reactive elements of the same character as the xed element and means for connecting them into the tank circuit and disconnecting them therefrom; means for amplifying and transmitting the Waves resulting from a selected one of said multiplications; a super-heterodyne receiving system having an intermediate frequency amplifier tunable over a certain band and a mixer delivering its output to the intermediate frequency amplifier; means for delivering waves of a selected predetermined multiplication to the mixer of the amplifying means; and means for delivering, in each case, displaced Waves of a different multiplication to the receiving system; and means for coordinating variation of the variable element in the oscillator tank circuit with the tuning of the intermediate frequency amplifier, the displaced Waves serving as the local heterodyning waves for said receiving system.

FRANK M. DAVIS. 

